The present invention generally relates to image transfer technology and, more particularly, to an apparatus and method for removing contaminants from photoconducting surfaces of liquid electrophotographic printing components after printing, and a liquid electrophotographic printer having the cleaning apparatus.
As used herein, the term “printer” generally refers to all types of devices used for creating and/or transferring an image in a liquid electrophotographic process, including laser printers, copiers, facsimiles, and the like.
In a liquid electrophotographic (LEP) printer, an electrostatic latent image is created on the surface of an insulating, photoconducting material by selectively exposing areas of the photoconducting surface to light (such as a laser). A difference in electrostatic charge density is created between the areas on the photoconducting surface exposed and unexposed to light. The electrostatic latent image is developed into a visible image using developer liquid, which is a mixture of solid electrostatic toners or pigments dispersed in a carrier liquid serving as a solvent (referred to herein as “imaging oil”). The carrier liquid may be conductive or insulative, depending upon the particular printing process. The toners are selectively attracted to the photoconductor surface either exposed or unexposed to light, depending on the relative electrostatic charges of the photoconductor surface, development electrode, and toner. The photoconductor surface may be either positively or negatively charged, and the toner system similarly may contain negatively or positively charged particles. For LEP printers, the preferred embodiment is that the photoconductor surface and toner have the same polarity.
A sheet of paper is passed close to the photoconductor surface, which may be in the form of a rotating drum or a continuous belt, transferring the toner from the photoconductor surface onto the paper in the pattern of the image developed on the photoconductor surface. The transfer of the toner may be an electrostatic transfer, as when the sheet has an electric charge opposite that of the toner, or may be a heat transfer, as when a heated transfer roller is used, or a combination of electrostatic and heat transfer. In some printer embodiments, the toner may first be transferred from the photoconductor surface to an intermediate transfer medium, and then from the intermediate transfer medium to a sheet of paper.
During the image transfer process, it is desirable that the developed image on the photoconductor surface is completely transferred off of the photoconductor surface. However, in an actual printing process, some of the developed image may not be completely transferred, leaving residual materials such as toner, imaging oil, charge directors and other dissolved materials on the photoconductor surface. The residual materials on the photoconductor surface reduce the print quality of subsequently printed images and shorten the useful life of the photoconductor surface. Therefore, there is a need to remove the residual materials from the photoconductor surface.
One existing device for removing residual materials from the photoconductor surface utilizes a wetting roller to place a layer of imaging oil (for example, an approximately 100μ layer of oil) on the photoconductor surface. A sponge roller subsequently is rubbed against the photoconductor surface to clean the surface and absorb the now dirty imaging oil and materials therein. A squeegee roller then squeezes the sponge roller to at least partially remove the dirty oil and materials therein from the sponge roller. Finally, a rubber blade is used to scrape the photoconductor surface and remove most of the remaining imaging oil from the photoconductor surface.
Although the described cleaning method does clean much of the residual material from the photoconductor surface, a layer of dirty imaging oil remains on the photoconductor surface. The dirty imaging oil contains charge directors and other dissolved materials that cause lateral conductivity on the photoconductor surface and that react with the printer environment to generate sticky materials that slowly but steadily coat the photoconductor surface. The print quality of the printer is thus adversely affected and the life of the photoconductor is shortened. It is desired to leave a cleaner layer of imaging oil on the photoconductor surface, and thus an improved apparatus and method for cleaning the photoconductor surface is desirable.